Case Studies: Laser & Optical Alignment

Case Study 1:
Repair, Laser Alignment and Dynamic Balancing of a 3500 hp Hammer Mill

Case Study 2:
Optical Alignment of Basin Agitator Shaft

Case Study 3:
Measuring Ball Mill Foundation Movement

Repair, Laser Alignment and Dynamic Balancing of a 3500 hp Hammer Mill

Problem: A large direct drive hammer mill was experiencing excessive main mill bearing and coupling failures. High vibration (over 3 inches, peak-to-peak) resulted in accelerated bearing housing wear. Bearing failures damaged the 80000 lb. rotor shaft and required extensive rework to put it back into service. The mill frame was severely worn. A new mill frame was being considered; however, a replacement mill cost over $1M and had a long lead time.

Investigation: The mill frame had both wallowed out mill anchor bolts and frame holes. The mill frame was observed to rack excessively with each rotation of the 80000 lb. rotor.

Measurement: Vibration was measured using an accelerometer, optical phototach and digital tracking filter. The vibration spectra contained multiple harmonics all with very high amplitudes.

Solution: The mill frame was shored up using old mill pins (4″ diameter) that were installed into holes that were core drilled into the mill’s concrete foundation. Strong-back clips were installed along the edge of each of the comers of the mill. Mill deflection and looseness was controlled. The mill was laser aligned and then dynamically balanced.

Results: Mill bearing failures were reduced. The mill replacement was deferred for over one year until which time other benefits prompted its replacement.

Optical Alignment of Basin Agitator Shaft

Problem: A water treatment facility was installing a new horizontal water agitating system in a existing basin. The system incorporated nine agitators wheels, all attached along a single 100 foot shaft. This shaft was supported by sleeve bearings every 10 feet. Bearing alignment was specified to be within ten thousands (0.01”) of a straight line. VESCO Incorporated was asked to measure and align the bearings.

Measurement: VESCO Incorporated was uniquely qualified for this project because they own some of the most accurate optical alignment equipment in the region. The sleeve bearings could be aligned using a parallel plate automatic level (0.0012 “/10’ accuracy) and optical theodolite (1 arc second accuracy).

Solution: The bearings were aligned better than the specification required. However, cost was less than the water treatment facility expected because of VESCO Incorporated’s efficient use of their high tech equipment.

Measuring Ball Mill Foundation Movement

Problem: A client of VESCO Incorporated had frequent problems with their large ball mill. The system was comprised of a motor, clutch, gearbox, twelve foot jack shaft, pinion gear, bull gear and ball mill. It seemed that over a period of time the pinion and bull gear would start meshing incorrectly, yet nothing had changed in the system. VESCO Incorporated laser aligned the entire system and the meshing was corrected, but then after a six month period the problem came back. Further investigation was necessary.

Investigation: VESCO Incorporated remeasured the alignment and sure enough it was out. By reviewing construction drawings of the mill foundation, it was concluded that the mill was slowly moving over time. The big question was how fast and how much.

Measurement: VESCO Incorporated installed permanent brass monuments into the mill foundation and pedestals. Using the most accurate optical theodolites available, the precise position of each pedestal was measured and recorded.

Results: Six months after the original measurement, VESCO Incorporated remeasured the position of the ball mill and compared it to the earlier data. The mill had in fact been moving and the direction and magnitude was quantified. The system was laser aligned taking into consideration the future movement so realignment only needed to occur every year instead of every six months. By diagnosing this problem early enough VESCO Incorporated saved their client over eighty thousand dollars,  which is the cost of a new bull gear.